Self-priming portable device

ABSTRACT

A portable powered device such as a tool, comprising a housing within which is defined a combustion chamber ( 8 ) for combustion of a mixture of fuel and a combustion-supporting gas, which mixture is compressed so as to be subjected to a pressure in excess of the ambient atmospheric pressure prior to combustion, combustion of the fuel/combination-supporting gas mixture providing the power by which the device performs its intended task, and wherein the combustion and/or a further combustive event provides the power to compress a successive fuel/combination-supporting gas mixture, such that a successive cycle of operation of the device may be performed without requiring manual compression of a fuel-combustion-supporting gas mixture by the user.

FIELD OF THE INVENTION

The present invention relates to a self-priming portable deviceincluding, but not limited to, a self-priming portable injection device,and a method of making the device. The device of the invention includesan internal combustion engine as a power source.

BACKGROUND OF THE INVENTION

It is well-known to provide hand tools with a power source. Typicallythe power source used is electricity, either from batteries or from amains outlet. However the prior art also discloses the use ofalternative power sources for tools and other hand-held implements.

For example, U.S. Pat. No. 6,045,534 discloses an injection device foradministering a medicament to a subject, the device being powered by apyrotechnic charge. WO 01/89612 discloses an injection device powered byan internal combustion engine.

In particular, WO 01/89612 teaches that the fuel/air mixture burnt inthe combustion chamber should preferably be compressed prior tocombustion. The document discloses in detail one way of effecting suchcompression, which relies on the user manually to depress a plunger. Thedocument also states that the process “may be effected automatically”but does not disclose any embodiment where compression of the fuel/airmixture is achieved automatically and it is not immediately apparent howthis could be done.

The present invention aims to provide a portable device powered by aninternal combustion engine in which a fuel/combustion-supporting gasmixture is compressed to a pressure in excess of the ambient atmosphericpressure, and wherein operation of the device is at least partlyautomated.

SUMMARY OF THE INVENTION

In a first aspect the invention provides a portable powered device suchas a tool, comprising a housing within which is defined a combustionchamber for combustion of a mixture of fuel and a combustion-supportinggas, which mixture is compressed so as to be subjected to a pressure inexcess of the ambient atmospheric pressure prior to combustion,combustion of the fuel/combination-supporting gas mixture providing thepower by which the device performs its intended task, and wherein thesaid combustion and/or a further combustive event provides the power tocompress a successive fuel/combustion-supporting gas mixture, such thata successive cycle of operation of the device may be performed withoutrequiring manual compression of a fuel/combustion-supporting gas mixtureby the user.

Preferably the fuel/combustion-supporting gas mixture is pressurised toa pressure of at least 2 bar, more preferably at least 3 bar. Typicallythe pressure will be in the range 3.5-6 bar.

In a first embodiment a single combustive event provides the power bywhich the device performs its intended task and also provides (directlyor indirectly) the power by which a successivefuel/combustion-supporting gas mixture is compressed for combustion in asubsequent cycle of operation. In an alternative embodiment a firstcombustive event provides the power by which the device performs itsintended task and a further combustive event (e.g. of a smaller dose ofthe fuel/combustion-supporting gas mixture, which may or may not becompressed prior to combustion) is required to compress a successivecharge of fuel/combustion-supporting gas for a subsequent cycle ofoperation. In such an embodiment the first combustive event willtypically occur within a main combustion chamber and the furthercombustive event will take place in a separate, subsidiary combustionchamber. (Note that the “further” combustive event may actually occurbefore the “first” combustive event.)

The powered device of the invention is preferably an injection device(needle-less or needle-based) for administering a dose of medicament toa human or animal (typically mammalian) subject. However, the devicecould be adapted to perform many different tasks or actions currentlypowered by other means such as motors or compressed air e.g. cutting,drilling, punching, screwing, hammering, spraying, pumping etc. As aspecific example, the inventors envisage the device potentially beingused as an alternative motive force for otherwise conventional airpistols or air rifles. However, for present purposes the invention willbe described in the context of an injector device.

The inventors have envisaged several different methods of achieving atleast semi-automation of the device. In the present context“semi-automation” means that one or more steps of the cycle of operationof the device are repeated automatically, in response to one or moreactuations of a trigger mechanism, and that at least one step of thecycle which is automated is compression of thefuel/combustion-supporting gas mixture. It should however be noted thatan initial cycle of operation may, depending on the embodiment, requirespecific manual user input—it is the subsequent cycles of operation inwhich the step is repeated automatically.

Desirably, as well as automatically compressing thefuel/combustion-supporting gas in the combustion chamber, the devicewill automatically repeat other steps of the operating cycle, such asre-dosing a dose of medicament (in those embodiments in which the deviceis an injector), automatically operating appropriate vents etc. to admitair or other combustion-supporting gas into the combustion chamber,exhausting combustion products etc.

In a preferred embodiment the device is fully automated (albeit possiblyrequiring an initial priming action on first use) in that one or moreactuations of a trigger mechanism enables the device to perform acomplete cycle of operation. If desired, the device could be arrangedsuch that the device will continue to perform cycles of operation whilstthe trigger is held, with an interlock mechanism of some kind to ensurethat a single cycle of operation is performed only when the device isactually positioned in contact with a subject, and that when removedfrom contact the operation of the device is interrupted. Whilst at leastsemi-automation of the device is an important feature of the invention,it will be advantageous to provide a manual override to allow a user toperform a cycle of operation manually (e.g. during an initial cycle forpriming, or to purge the device after use or clear blockages ormis-fires etc).

The device will advantageously comprise an interlock or other safetymechanism to reduce the likelihood of accidental discharge and preventthe device from firing unless properly primed. In particular it may bedesirable to have a multi-stage actuation or triggering sequence. Forexample, a trigger mechanism provided on the device may have a pluralityof discrete sections of travel, passage therethrough actuating varioussteps of the operating cycle. Alternatively, the trigger may bedepressed fully (or substantially so) a plurality of times, eachdepression of the trigger causing actuation of different parts of theoperating cycle. Yet a further arrangement is for a single actuation ofthe trigger being sufficient to initiate a cycle of operation, but thatvarious parts of the cycle are subject to delay (by mechanical and/orelectrical means) and that one or more sensors can interrupt or preventparts of the cycle from occurring if conditions are not appropriate(e.g. no medicament in the medicament chamber, or the orifice of thedevice is not in contact with a subject). The interlock or interruptmechanism may conveniently be operated by or dependent on input/feedbackfrom the state of the trigger and/or a nozzle guard (e.g. depressed orreleased).

In one embodiment a combustive event in the combustion chamber actsdirectly or indirectly on two separately movable pistons: a work pistonwhich, directly or indirectly, performs the work (e.g. expulsion of adose of medicament from the device); and a priming piston which servesto compress the fuel/combustion-supporting gas mixture prior tocombustion, the priming piston being movable between a primed positionat one end of its stroke and an exhaust position at the other end of itsstroke, and wherein both the work piston and the priming piston aremovable in response to the combustive event in the combustion chamber.In one arrangement the work and priming pistons move in opposeddirections in response to the combustive event in the combustionchamber. In an alternative arrangement the work and priming pistons movein the same direction in response to a combustive event in thecombustion chamber.

In a preferred embodiment, which may preferably be combined with thefeatures described in the preceding paragraph or may be employedseparately, there is provided a movable baffle member which communicateswith the combustion chamber and forms a gas-tight seal with the innersurface of the housing, the baffle member comprising a one-way valvemeans which valve means permits entrance of the combustion-supportinggas into the combustion chamber but does not permit egress of combustionproducts, the baffle member being movable from a first position to asecond position in response to a combustive event within the combustionchamber; the device further comprising a return means to return thebaffle member from the second position to the first position, whichreturn movement exhausts the combustion products from the combustionchamber. The baffle member may conveniently take the form of a baffleplate and/or be incorporated into the work piston.

The return means may comprise any convenient means of returning thebaffle member, such as a spring (especially a constant force spring), awasher, compressed air, or a further combustive event.

Where the device of the invention is an injection device, the devicewill comprise further operating features which may conveniently begenerally as detailed in WO 01/89612, the content of which isspecifically incorporated herein by reference.

The combustion-supporting gas may be oxygen or other gas comprisingoxygen. Conveniently the combustion-supporting gas will be air.

The device as a whole is typically of such dimensions as to be readilyhand-held in use. The barrel needs to be stable at fairly hightemperatures and strong enough to withstand the high pressures generatedduring operation of the device, but is also desirably of low density inorder to minimise the weight of the device. The barrel or housing ispreferably formed from heat-resistant plastics material or metal (e.g.an aluminium alloy). The device will comprise means for forming acombustible mixture of fuel and air or other combustion-supporting gasin the combustion chamber and will generally comprise a fuel inlet and aseparate air inlet. One or both of these inlets may conveniently beprovided with valve means to regulate the flow of fuel or air, as thecase may be.

The fuel is advantageously one which is gaseous at atmospheric pressure(760 mm Hg) and room temperature (20° C.) but which can be caused toliquefy at room temperature by mildly elevated pressure. Examples ofsuitable fuels include butane (which is commonly used as a fuel indisposable cigarette lighters) and propane. Desirably therefore the fuelis held as a liquid, under pressure, in a fuel reservoir.

In preferred embodiments of the invention the device provides asubstantially consistent power output from one combustive event to thenext. In order to achieve this desired objective, it is advantageous toensure that a consistent amount of fuel is present in the combustionchamber for each combustive event. Accordingly, in preferredembodiments, the device comprises means for introducing an accuratelypre-determined amount of fuel into the combustion chamber for eachcombustive event.

Accordingly, in a preferred embodiment the device of the inventioncomprises a fuel dosing assembly for metering a dose of fuel from areservoir of liquefied gas fuel to be delivered to the combustionchamber, wherein the dose of liquefied gas fuel is accurately meteredwithout undergoing a partial phase change. Specifically, in preferredembodiments, the fuel is metered through metering means whilst in theliquid phase, but allowed to vaporize upon expansion on entry into thecombustion chamber (typically at atmospheric pressure at this stage ofthe cycle).

By way of explanation liquefied fuels such as propane and butane tend tovaporize as soon as they are removed from the elevated pressure underwhich they are stored. The inventors found that this phase changerendered it extremely difficult to meter an accurate dose of fuelconsistently. Accordingly, in preferred embodiments it is desired that aliquefied gaseous fuel is measured and dosed whilst still under pressure(and thus in liquid form), which allows for far greater consistency offuel dosing. Conveniently the fuel dosing assembly comprises a spoolvalve or a rotary valve, and suitable arrangements are disclosed in WO01/89612. Alternatively a shuttle valve, of the type employed inpressurised metered dose inhalers, could be employed. The fuel dosingassembly valve or valves may be mechanically or electronically driven.

In preferred embodiments of the device of the invention, the fuelreservoir is pressurised, at a substantially constant pressure, which iseffective in keeping all of the fuel in the reservoir in liquid form.Such active pressurizing means may comprise, for example, a spring meansacting on a movable pressure plate or piston within the fuel reservoir.

In order to optimise the consistency of power output of the engine, itis desirable that the device will comprise priming means for introducingan accurately pre-determined amount of oxygen, air, or othercombustion-supporting gas, into the combustion chamber before eachcombustive event, or at least ensuring that a large proportion (over75%, preferably over 85%, more preferably over 95%) of the combustionproducts are exhausted from the combustion chamber before a successivecombustive event occurs, and allowing the exhausted products to bereplaced by a corresponding volume of combustion-supporting gas. Inparticular (but not essentially) it is desirable that the device of theinvention includes both a priming means for introducing an accuratelypre-determined amount of oxygen or air etc, and a fuel dosing means (asdescribed above) for introducing an accurately pre-determined amount offuel, into the combustion chamber prior to each combustive event. Ifdesired, a source of combustion-supporting gas may be provided with orincorporated into the device (e.g. a cylinder of compressed air).

For the avoidance of doubt, it should be stated that in someembodiments, the amount of fuel and/or air (or othercombustion-supporting gas) introduced into the chamber can be alteredbetween predetermined, fixed amounts. Thus, the power output of thedevice is consistent for a given volume of fuel and air, but these canbe adjusted as desired, to increase or decrease the power output of thedevice between pre-determined set values. Thus, for example, the fueldosing assembly may be arranged to meter one of several, fixed amountsof fuel. Preferably the fuel and/or air inlets, by which the fuel andair (or other combustion-supporting gas) are respectively introducedinto the combustion chamber, will be shaped so as to set up turbulentflow, facilitating mixing of the fuel and air upon entry into thecombustion chamber. Forcing fuel and/or air through one-way valve meansprovided in a baffle plate member is one convenient method ofestablishing turbulent flow and/or causing thorough mixing.

It will be apparent that in a device in accordance with the inventiondefined above, in which the combustion chamber is pressurised prior toignition of the air/fuel mixture, such superatmospheric pressure wouldtend to displace the piston or pistons communicating with the combustionchamber. In order to resist this the device preferably comprises arestraining means, acting directly or indirectly on the piston/pistons,which serves to keep the piston/s in place against the pressure of thecompressed air/fuel mixture, but which is insufficient to restrain thepiston when the air/fuel mixture is ignited. In one embodiment thedevice is provided with one or more spring-biased fingers, typicallymounted or acting generally perpendicular to the direction of travel ofthe piston, which fingers engage co-operatively shaped recesses on thepistons or associated shaft, the spring-biasing acting to urge thefingers into engagement with and thereby restrain, the piston orassociated shaft. In an alternative embodiment the restraining membertakes the form of a resiliently-deformable, or a rupturable, retainingdevice. An example of a rupturable retaining device is a shear pin, orsimilar, which can secure the piston (or work member). In anotherembodiment the restraining means comprises one or more strutsspring-biased, resiliently deformable or deflectable, so as to bedisplaceable, mounted generally parallel to the direction of travel ofthe piston, but with an angled surface at the upper end proximal to thepiston, the strut or struts being displaceable outwards by the pistonupon combustion. Preferably the restraining means automatically re-setsafter each cycle of operation—accordingly a shear pin is a lesspreferred arrangement than a resiliently deformable or deflectablemember.

The ignition means conveniently takes the form of a spark plug. This maybe powered by a piezoelectric ignition circuit e.g. of the typedisclosed in EP 0316468. In preferred embodiments the ignition meanswill be interlocked such that it is inoperable unless the rest of thedevice is in a primed state ready to fire. A further preferred featureis that the ignition means can be disabled as soon as combustion hascommenced, in order to conserve electrical energy. It may also bedesired to limit the electrical output of the ignition means to belowthe breakdown voltage of the spark gap, and then initiate sparkformation in a controlled manner. Controlled ignition may be achieved,for example, by means of a pulse transformer (as used in electronicflash apparatus) or by means of a piezoelectric spark generator, itselfinsufficient to cause ignition but capable of opening an ionization pathfor the main spark to follow. Typically the ignition circuit willcomprise one or more capacitors and a voltage transducer coil. It ispreferred that the spark voltage/power is maintained at a substantiallyconstant value, as this has an effect on the consistency of thecombustion in the combustion chamber.

A device in accordance with the invention will generally comprise one ormore further components associated with a conventional internalcombustion engine. In particular, the device will conveniently compriseat least one exhaust outlet to allow the products of combustion to exitthe combustion chamber.

The device may be used to deliver a medicament to a human subject or toany animal subject, including birds (especially poultry), farm livestock(such as sheep, pigs, cattle, goats, horses), and companion animals(especially cats and dogs). It is desirable to minimise the noise ofoperation of the injection device to avoid discomfort or irritation tothe recipient of the medicament, and any nearby people or animals. Theinventors have noted that, in this respect, it is desirable that theresidual energy of the products of combustion is at least largelydissipated before the exhaust valve is opened, so that venting of thecylinder following combustion is accomplished quietly.

Desirably the exhaust valve or valves are closed throughout theinduction, compression, ignition and power delivery phases of theoperating sequence and the exhaust valve opens only once the combustionhas been completed and all movement (downstroke or upstroke) of the workpiston ceased. In one embodiment this is achieved as part of a manualoperating sequence, and may typically be the penultimate step of thesequence prior to resetting the piston, ready for storage of the deviceuntil it is to be used again. Alternatively, the exhaust valve may beopened automatically (e.g. a determined length of time after ignition).In either event it is preferred that a locking mechanism preventspremature opening of the exhaust valve. Timing and actuation of thevalves may be mechanical or electrical.

The device will also further advantageously comprise return means, toreturn the work piston to a primed position when the device has beenfired. The return means may comprise a simple spring biasing means, suchas a compression spring which is compressed by the stroke of the pistonsuch that, when the force on the piston from the compressed spring isgreater than the force exerted by the gaseous post-combustion products,the piston will tend to return to its primed position (once the exhaustvalve or valves have opened). Alternatively, or additionally, thedepression of the piston can be used to compress gas in a compartmentbeneath the piston, thus leading to an increase in pressure actingupwards on the piston which, when it becomes greater than the downwardpressure of the combustion products acting on the piston, will tend toreturn the piston to its primed position. An arrangement incorporatingboth of these features is disclosed in EP 0 316 468.

The work member typically takes the form of a metallic (e.g. steel)piston rod or push rod welded, screw-threaded or otherwise operablylinked with the piston. It should be noted that it is not essential forthe work member to be rigidly attached, or physically connected, to thepiston. For example, the operable linkage between the piston and thework-member could take the form of a hydraulic fluid-filled conduit, thehydraulic fluid in the conduit serving to transfer energy from thepiston to the work member. Additionally or alternatively, one or moresolid intermediate members may be disposed between the piston rod andthe work member. Such an intermediate solid member may be generallyreferred to as a “striker”. In such an arrangement the piston or pistonrod never comes into physical contact with the work member. A preferredarrangement provides a temporary separation (e.g. a small, air-filledgap) between the piston rod and the work member and/or any intermediatestriker—the piston initially being separated from the work member orintermediate member when the device is primed, which separation allowsthe piston to reach a higher velocity (following combustion) beforecontacting the work member and/or intermediate member. Accordingly,greater initial acceleration is conferred on the work member than wouldhave occurred if the piston was in physical contact (or otherwiserigidly-linked) with the work member at all times.

It is particularly envisaged that the device of the invention may beused as a means to administer a medicament to animals or to use in massvaccination/inoculations of human subjects (e.g. in schools,universities, work places or other large institutions).

It will normally be preferred that the device of the invention willperform only a single combustive event when the trigger is actuated soas to avoid, for instance, inadvertent repeated injection of a subject.It will, however, be preferred that the device is provided withsufficient reserves of fuel and (if appropriate) electrical energy thatit will be capable of performing a plurality (e.g. a minimum of 1000 or2000) firing cycles before the fuel and/or electrical energy reserves(if present) are exhausted.

The medicament chamber of the device may contain sufficient medicamentfor just a single dose for delivery to the subject, so as to requirereplenishment with medicament after delivery of each dose of medicament.Alternatively, the medicament chamber may contain sufficient medicamentfor a plurality of doses, such that only occasional replenishment isrequired. In the latter situation, the medicament chamber willconveniently be provided or associated with dosing means, such that anappropriately-sized, measured dose of medicament is delivered each timethe device is used. Desirably the dosing means is adjustable betweendifferent positions so that various pre-determined doses of medicamentmay be delivered.

The medicament chamber may form an integral part of the device of theinvention, or may take the form of a readily removable component.

Needleless injectors per se are well known to those skilled in the art.Examples of such devices include those disclosed by Schwebel et al,which are powered by a pyrotechnic charge (see U.S. Pat. No. 3,802,430;U.S. Pat. No. 4,089,334 and U.S. Pat. No. 4,124,024).

It is desirable that devices such as needleless injectors have aconsistent power output: whilst, on one hand, sufficient power must beprovided to force the medicament or other substance through the skin, itis necessary to avoid the use of too much power, otherwise the substancemay be injected deeper than is required and may cause greater disruptionto the tissues (especially blood vessels) of the subject than isrequired, leading to extensive and unsightly bruising, and cause pain.

Those skilled in the art will be acquainted with the types and doses ofsubstances which are deliverable by a needleless injector. A typicaldose volume will be between 0.01 ml and 2.0 ml. The substance to bedelivered may take the form of a liquid (a solution or suspension), butother formulations may be employed.

Ideally, in order to reduce or minimise sensation of pain associatedwith the injection, the medicament should be administered within aninjection interval of less than 500 milliseconds, preferably about 200milliseconds. Further, in an ideal embodiments, there is an initial peakin the injection force provided by the injector in order to overcome theresistance provided by the subject's skin, followed by a longer,sustained force of lower magnitude to deliver the medicament dose. Theinitial penetrating force is typically in the range 0.4-1.4 Newtons, andthe medicament delivery force is advantageously in the range 0.2-0.8Newtons.

An injection device orifice, through which the medicament is expelled,will conveniently have a diameter in the range 0.1-0.5 mm, morepreferably in the range 0.12-0.45 mm. An orifice of these dimensions,with average forces of the magnitude described above, would create aninitial medicament velocity of about 120 m/s to penetrate the skin, withthe rest of the medicament dose being delivered at a velocity of about70 m/s. A preferred velocity is in the range 50-150 m/s, which is foundsuitable for transdermal delivery of most or all of an average dose ofmedicament to a typical human subject.

In a second aspect the invention provides a portable tool which performsa cyclical operation, typically an injector device, comprising amulti-component work member assembly, which components after performanceof one cycle of operation are automatically returned to their startingpositions ready for performance of another cycle. Desirably the tool ofthe second aspect of the invention will be generally in accordance withthe tool of the first aspect defined above.

In particular, the work member assembly will typically comprise a workpiston rod or similar, an intermediate striker member and an end workmember (such as a plunger). Typically the work piston rod and theintermediate member will be co-axially mounted, conveniently on a commonguide means such as a shaft or linkage, which may typically pass througha central bore provided in both the work piston rod and the intermediatemember.

Advantageously the components of the work assembly are such that, at thestart of the cycle the intermediate member is in spaced apartrelationship with the end member and also with the work piston rod.During operation of the device, the work piston accelerates over thecentral shaft moving relative thereto. After a short period of travelthe end of the work piston rod contacts the intermediate member, and thetwo latter components move together, relative to the central shaft,until they contact the end member, forcing the end member to perform thedesired end task (e.g. expulsion of a medicament from a chamber). Afterreaching the end of its stroke, the work piston rod commences its returnstroke under the influence of a return means. However the work pistonrod does not immediately engage the central shaft, so that a spacedapart relationship with the intermediate member is re-established.

In a convenient embodiment the intermediate member comprises aparamagnetic or, more preferably, ferromagnetic material, and apermanent magnet or electromagnet provided on or in the device applies aweak magnetic force sufficient to compel the intermediate member to takeup a position between the end member and the work piston rod in spacedapart relationship therefrom.

In a further aspect the invention provides a method of administering amedicament to a human or animal subject, the method comprising use of aninjector device in accordance with the first or second aspects of theinvention defined above.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described by way of illustrativeexample and with reference to the accompanying drawings, in which:

FIGS. 1 and 2 a are longitudinal sections of an injector device inaccordance with the invention, the section of FIG. 2 a being at 90° tothe section of FIG. 1;

FIG. 2 b illustrates one example of an exhaust valve means forincorporation in the device of the invention; and

FIGS. 3 a-c are a series of longitudinal sections of a differentembodiment of an injector device in accordance with the invention,showing three stages, a, b and c respectively, in the operation of thedevice.

DETAILED DESCRIPTION OF EMBODIMENTS

A first embodiment of a device in accordance with the invention takesthe form of a needle-less injector for administering a dose ofmedicament to a human or animal subject, and is depicted in longitudinalsectional view in FIGS. 1 and 2 a.

Referring to those Figures, the injector comprises a housing in the formof generally cylindrical barrel 2, formed from aluminium. Disposedtowards one end of the barrel 2 is a nozzle assembly indicated generallyby reference numeral 4 and disposed towards the opposite end of thebarrel 2 is a priming assembly indicated generally by reference numeral6. Within the barrel 2 is a combustion chamber 8 defined at one end by abaffle plate 10 associated with a priming piston 12, and defined at theother end by a work piston 14. When the device is primed, a combustiblemixture of fuel/combustion-supporting gas is held within the combustionchamber 8, at a pressure in excess of ambient atmospheric pressure.

The device also includes (shown in varying degrees of detail) anignition means for igniting the combustible mixture in the combustionchamber, a trigger mechanism for actuating the ignition means (andoptionally actuating other components of the device also), an exhaustsystem for venting the products of combustion from the combustionchamber 8, fuel and air inlet means for introducing fuel and air orother combustion-supporting gas into the combustion chamber 8.

The various components of the device and its operation will now bedescribed in more detail. The embodiment depicted in FIGS. 1 and 2 a isappropriate for the delivery of a 2 ml dose of medicament, using jetpressures (at the nozzle of the instrument) in excess of 300 bar. Theinner bore of the barrel 2 is 36 mm in diameter, and the overall lengthof the complete device is about 300 mm.

The priming assembly 6 comprises a lever 16 (for initial manual primingof the device), associated gear wheels 18 a, b, one of which (18 b)engages with a ratchet surface of a priming tube 20. Inside the primingtube 20 is a priming shaft 22, mounted at one end of which is thepriming piston 12. A priming spring 24 is seated within an annularrecess on the rear face of the priming piston 12 and extends, within thebarrel 2 towards the rearmost end of the barrel. In general terms, the“front” end of the device may be considered as the end region comprisingthe nozzle assembly, and the “rear” end may be considered as the endregion comprising the gear wheels 18 a,b.

Associated with the priming assembly is the baffle plate 10 and a bafflepiston 26. The baffle plate 10 is a circular flange mounted at one endof the baffle piston 26 which is itself located within a circular boreprovided in the priming shaft 22. A baffle spring 28 is located betweenthe rear face of baffle plate 10 and the front face of the primingpiston 12. A deep annular recess is provided in the priming piston 12 toaccommodate the baffle spring 28. The baffle spring 28 acts to urge thebaffle plate 10 towards the combustion chamber 8. A gas-tight seal isprovided between the edge of the baffle plate 10 and the inner surfaceof the barrel 2. The baffle plate 10 is provided with one-way valvemeans which permits entrance of combustion-supporting gas (in thisinstance, air) into the combustion chamber 8 but does not permit theegress of combustion products. In the embodiment illustrated the one-wayvalve means comprises a plurality of 2 mm diameter valve holes drilledthrough the baffle plate 10, which holes are covered by a thin,stainless steel valve plate. The valve plate can lift off the baffleplate 10 in response to a positive pressure differential to the rear ofthe baffle plate 10, allowing combustion-supporting gas to enter thecombustion chamber 8. In contrast, a positive pressure differentialinside the combustion chamber 8 forces the valve plate against thebaffle plate 10, closing the valve holes, preventing egress ofcombustion products from the combustion chamber 8.

The baffle plate 10 and baffle piston 26 are movable relative to thepriming piston 12 and priming shaft 22.

The nozzle assembly 4 comprises a nozzle guard 30, a dosing chamber 32to contain a dose of medicament to be injected, the work piston 14, awork piston spring 34 seated between the work piston 14 and the frontend of barrel 2, and an orifice or nozzle 31.

Actuation of the device causes the work piston 14 to move forward athigh velocity, so as to encounter striker 36. This in turn acceleratesthe striker 36 to act on plunger 38, forward movement of which expelsthe dose of medicament from the dosing chamber 32 through orifice 31 andinto the subject.

As explained above, the fuel/combustion-supporting gas mixture in thecombustion chamber 8 is pressurised in excess of ambient atmosphericpressure prior to combustion. Accordingly it is necessary to provideretention means to act so as to keep the baffle plate 10 and/or the workpiston 14 (preferably both) in place, against the excess pressure in thecombustion chamber 8, when the device is in the primed condition. In onearrangement a single retention means may be provided to act (directly orindirectly) on both the baffle plate 10 and the work piston 14. In analternative arrangement, a separate retention means is provided to acton the respective components mentioned above. In the embodimentillustrated in FIGS. 1 and 2 a, a trigger/latch mechanism (denotedgenerally by reference numeral 40 in FIG. 2 a) is provided which(together with the action of priming spring 24), indirectly, acts toretain the baffle plate 10 in place when the device is primed; and thework piston 14 is retained partly by the action of work piston spring 34but primarily by deflectable metal struts, two of which (42) are shownin FIG. 1.

The operation of the device as a whole, and of particular componentstherein, will now be described in detail.

Upon first use of the device, a manual priming operation must beperformed for the initial cycle, in order to generate the pressurisedmixture of fuel/combustion-supporting gas in the combustion chamber 8.In the embodiment shown in FIGS. 1 to 3 the combustion-supporting gas isair.

Referring to FIG. 1, operation of the priming lever 16 drives a train ofgear wheels 18 a,b which in turn draw back the priming tube 20 out ofthe rear of the barrel housing. The priming tube 20 in turn retracts thepriming shaft and priming piston 12 to a point where an accommodatingrecess on the priming piston 12 enters into a snap fit engagement withthe latch of trigger latch mechanism 40 and is retained. The primingtube 20 is then pushed back inside the barrel 2, where it is positionedduring subsequent operation of the device.

It is advantageous, to simplify operation, that the forces involved inpriming the device are not too high. Accordingly, it may be beneficialto allow air to enter during the retraction of the priming piston 12,otherwise the manual priming must do work in creating a partial vacuumbetween the piston 12 and the baffle plate 10. A number of ways can beenvisaged to allow air to enter the combustion chamber 8 in a controlledmanner e.g. allowing air to flow forwards into the combustion chamberpast the seal provided around the priming piston 12 in a one-way manner,or to incorporate a check valve in the baffle plate 10, such that alimited flow of air can pass backwards across the baffle plate for lowpressure differentials (i.e. not during combustion). Yet anotherapproach might be to allow one or more exhaust ports to be open duringpriming, allowing air into the combustion chamber 8 such that the baffleplate 10 can move backwards with the priming position 12—the bafflespring 28 would then act to return the baffle plate 10 to its desiredposition.

The space vacated by the retraction of the priming piston 12 is filledwith air at atmospheric pressure, and the exhaust port or ports of thedevice are closed. On an initial partial actuation of the triggermechanism 40 (shown in FIG. 2 a), fuel for the combustionprocess—typically butane but potentially also other appropriate fuelssuch as propane, or a mixture of such fuels—is introduced into thecombustion chamber 8. In the current embodiment this is via the releaseand expansion into the chamber 8 of fuel held under pressure in theliquid phase. In an alternative arrangement fuel is introduced into thevolume behind the baffle plate 10 and forced therethrough into thecombustion chamber 8, thereby aiding mixing.

On further depression of the trigger, the trigger mechanism 40 releasesthe trigger latch which in turn releases the priming piston 12. This isdriven towards the baffle plate 10 through the action of a compressivecomponent or components—in this case the priming spring 24—and in theprocess it forces the air in front of it through the baffle plate 10non-return valve into the combustion chamber 8. (Seals prevent the flowof air between the priming piston 12 and the baffle piston 26, andbetween priming piston 12 and the inner surface of the barrel 2.)Because of the pressures and contact forces involved and the desire tokeep the device as small as practically possible, it may be advantageousfor the trigger mechanism to give mechanical advantage such that theactuation force is not too high. This can be achieved in a number ofways, such as through the inclusion of linkages and/or levers.

As the priming piston 12 is pushed to its forwardmost position,contacting the back face of the baffle plate 10, the pressure in thecombustion chamber rises to a specific predetermined value. This can becontrolled through selection of the appropriate travel geometries andcombustion chamber volume, and is typically of the order of 2-6 bar forthe configuration described. The work piston 14 is secured in placeagainst the combustion chamber 8 during this action by a combination ofthe work piston spring 34 and an additional re-settable releasemechanism which, in the embodiment depicted, takes the form of twodeflecting metal release struts 42 which deflect to release the pistononce a given load threshold is reached and return to the engagedposition as the piston returns. Further depression of the triggerculminates in an action (in this instance, the closing of a switch in anelectrical circuit) which generates a spark via one or more spark plugswhich protrude into the combustion chamber 8. Given a spark ofsufficient power and voltage, generated by an ignition circuitincorporated within the device, ignition of the pressurised fuel/airmixture occurs, leading to rapid combustion.

As combustion occurs, pressure within combustion chamber 8 risesrapidly. This results in an increase in the forward force on the workpiston 14 but the piston is prevented from moving any significantdistance forward by the release struts until the pressure reaches atarget value. At this point the struts 42 deflect, releasing the workpiston 14 which then moves forward rapidly under the increasing pressureof combustion.

The combustion process also causes re-setting of the priming system. Inthe illustrated embodiment, the expanding gases are prevented frompassing back through the holes in the baffles plate 10 by the non-returnvalve means. Hence the pressure drives the baffle plate 10 and primingpiston 12 back towards the rear of the device, against the resistiveforces of the priming spring 24 (and, if appropriate, a second releasemechanism). The baffle plate 10 and priming piston 12 are pushedbackwards to the point where the priming piston passes the triggerlatch(es) which deflects and then springs back so as to secure thepiston 12 in the primed position. Note that the mechanism must be suchthat this occurs even if the trigger is still being held in the ‘fire’position. In this location, a priming piston seal now lies just behindsmall air inlet apertures (denoted by reference numeral 11) in thebarrel 2 (shown in FIG. 2 a, immediately in front of the latch) whichhence allow the entrance of the air charge for the next operationsequence.

The baffle plate 10 however is not latched in place and is pushed backtowards the combustion chamber 8 by the baffle spring 28. In so doing,the baffle plate 10 tends to compress the combustion products retainedwithin the sealed combustion chamber. Combustion products are alsocompressed by the work piston 14 which begins its return towards itshome position, urged by the work piston spring 34.

The combustion products are exhausted and the baffle plate 10 and workpiston 14 return fully to their home positions when the exhaust port(not shown) is opened. This can occur as soon as the full forward actionof the work piston 14 and plunger 38 and the re-priming action of thepriming piston 12 have taken place, and may be time accordingly. One wayof achieving this is to link the state of the exhaust port to theposition of the sprung nozzle guard 30 which is maintained in theextended position until just before firing when the action of theoperator pushes the guard into a retracted position by applying a forceagainst the subject. When the nozzle guard 30 is depressed, the exhaustvalve is closed and combustion can take place, but when the guard 30 isreleased (just after firing) by removing the nozzle guard 30 fromcontact with the subject the exhaust port returns to its normally openstate, allowing expulsion of combustion products from the chamber 8 bythe returning priming and work pistons 12, 14 respectively.

FIG. 2 b illustrates one possible exhaust port configuration, where anexhaust block 50 is provided with a guide tube 52. Running axiallywithin guide tube 52 is a shaft 54 which drives an exhaust valve shuttle56 against a spring 58. Two seals 60 prevent flow of gases between thevalve shuttle 56 and the inner bore of exhaust block 50 and guide tube52.

The assembly shown is fixed on the side of the main barrel 2 with a port62 connecting the combustion chamber 8 to the open bore in the exhaustblock. The normally open exit route from this bore is via a bore throughthe valve shuttle 56 and out through a side port (not shown). When thenozzle guard 30 is depressed, a linkage to the shaft 54 forces the valveshuttle 56 to move into the block 50, compressing the spring 58 andmoving the innermost seal 60 beyond the exhaust exit bore which now liesbetween the two seals, thus closing the exit route for any gases in thechamber 8. When the nozzle guard 30 is released, the spring 58(potentially in conjunction with a further spring on the guard itself)returns the shaft 54 and valve shuttle 56 to the normal position,opening the valve. In other configurations the exhaust port state couldbe linked to other parameters such as trigger positioning or timingcircuits.

The work piston and other ‘dose delivery’ components are alsoself-positioning as part of the re-priming process. For a single workpiston/plunger component this is readily accomplished as the return ofthe work piston will automatically re-position the plunger to which itis fixed. For configurations, such as that illustrated in FIGS. 1 and 2a, in which energy from the combustion event in combustion chamber 8 istransmitted to the dosing chamber 32 by a train of components, automaticself-positioning is more complicated.

In the embodiment shown, self-positioning of the dosing assembly isachieved by having the plunger 38 connected to the work piston 14 via arigid linkage 37 which runs freely through the center of the work piston14 and also the striker 36. When, during combustion the work piston 14accelerates forward initially, it passes freely over the linkage 37 andhence plunger 38 and striker 36 do not move. It is only when the frontface of the work piston 14 strikes the back face of the striker 36 thatthese components begin to move forward, separately at first but thencoalescing together to form a single unit. The combined work piston14/striker 36 then impact on the rear face of plunger 38, pushing itthrough the dosing chamber 32 and thereby expelling a dose ofmedicament. On its return the work piston 14 does not pick up thelinkage 37 immediately and hence the gap between piston 14 and plunger38 and striker 36 is re-established. The striker 36 is pushed or pulledinto position in between the piston 14 and plunger 38 by an externallyapplied force e.g. from one or more magnets housed in the dose chamber32.

Refilling of the dose chamber 32 also takes place automatically. Whenthe work piston 14 pulls the plunger 38 back, a check valve in thenozzle prevents air being drawn in through the orifice. The resultingsuction instead draws a new dose of medicament through a feed line froma dose reservoir (either a bottle, held within the device, or a hoseline to separate tank). A check valve in this feed line close to thedose chamber inlet prevents back flow of dose during actuation.

A different embodiment of the invention is shown in FIGS. 3 a-c. Theembodiment employs many of the general features of the embodiment shownin FIGS. 1 and 2 a, i.e. an injector device in which an internalcombustion engine is used to provide the motive force to expel a dose ofmedicament through an orifice into a subject and wherein the devicecomprises both a work piston 14 and a baffle plate 10. Thus, wherecomponents are functionally equivalent to those illustrated in FIGS. 1and 2 a the same reference numerals are employed.

Referring to FIG. 3, an injector device comprises a generallycylindrical housing in the form of a barrel 2, within which is provideda priming piston 12 mounted on a priming piston shaft 22, and a baffleplate 10, which are movable relative to one another. The baffle plate 10is mounted on a work piston 14 which is received within a central boreprovided within the priming piston shaft 22.

As in the previously described embodiment, the priming piston 12 andbaffle plate 10 are provided with appropriate sealing means to form agas tight seal with the surfaces over which they move, and baffle plate10 is additionally provided with one-way valve means which permitsentrance of a combustion-supporting gas (in this instance, air) into themain combustion chamber 8, but which does not permit the egress ofcombustion products. The main combustion chamber 8 is defined at one endby the surface of baffle plate 10 and at the other end and sides by thebarrel 2. The device also comprises a subsidiary combustion chamber 72.Both the main and subsidiary combustion chambers 8, 72 are provided witha respective spark plug. The subsidiary combustion chamber 72 is at theopposite end of the barrel to the main chamber 8, and is defined by thesurface of priming piston 12 at one end region and at the opposed endregion by the barrel 2.

FIGS. 3 a-c show sequential stages in operation of the device. In FIG. 3a the device has been fired and the priming piston 12 has reached theend of its stroke; the baffle plate 10 and plunger 38 have returned tothe positions they assumed prior to firing. In the case of the baffleplate 10, the return is mediated by a return means in the form of abaffle plate spring (not shown) provided between the rear face of thebaffle plate 10 and the front face of the priming piston 12. All thevalves are closed, there is a dose of medicament in the dosing chamber32 and there is air at atmospheric pressure in both main and subsidiarycombustion chambers 8, 72 and in the volume 74 between the baffle plate10 and priming piston 12.

Liquid fuel is then metered into the device where it evaporates tobecome gaseous. This can either be done by having two separate fuelreservoirs and metering valves operated simultaneously or, morepreferably, through a single reservoir and metering valve whereby thetotal amount of fuel required is metered into a feed chamber and thenreleased into the device such that the chambers 8, 72 fill to equalpressure. Relative volumes of the main and subsidiary combustionchambers will ensure that the correct amount of fuel is introduced intothe two chambers 8, 72. The fuel may be metered directly into therespective combustion chambers 8, 72, or may be metered into the deviceand then indirectly introduced into the combustion chambers. In apreferred arrangement, fuel for the combustion chamber 72 is metereddirectly into the chamber, whilst fuel for chamber 8 is metered into thevolume 74 and then forced through valve means in baffle plate 10 intothe chamber 8, which arrangement facilitates mixing of the fuel and air.

The subsidiary combustion chamber 72 now contains a gaseous mixture offuel and air at atmospheric pressure (FIG. 3 a). On sparking of thecorresponding spark plug this mixture is ignited and combustion occurs.This results in rapid expansion of the gases in the chamber 72 whichdrives the priming piston 12 backwards towards the baffle plate 10,compressing the baffle plate spring (not shown) and forcing the airthrough the one way valve(s) in baffle plate 10 into the main combustionchamber 8. Seals on the mating shafts prevent the compressed air passingbetween the baffle plate 10 and the priming piston 10. Seals on theouter diameters prevent flow of air between priming piston 12 and/orbaffle plate 10 and the barrel 2. The main combustion chamber 8 nowcontains a pressurised gaseous fuel/air mixture which may be atpressures typically between 2 and 6 bar (FIG. 3 b), so that the deviceis primed.

On sparking of the second spark plug, the timing of which can begoverned by the ignition circuit employed, combustion takes place in themain combustion chamber 8, and the combination of baffle plate 10/workpiston 14 and priming piston 12 are driven rapidly forwards.Simultaneously, or very shortly afterwards, a valve (or valves) on thesubsidiary combustion chamber 72 is opened and this allows thecombustion products in the subsidiary combustion chamber 72 to beexhausted, preventing the build up of retarding forces on the primingpiston 12. The operation and timing of this valve may be mechanical orelectrical e.g. through the use of a solenoid valve driven from the mainignition circuit. As the baffle plate 10 moves forward, the linkagesbetween it and the plunger 38 result in an amount of lost motionfollowed by rapid forward motion of the plunger 38. In the case of theinjector application shown, this would result in the dose of medicamentbeing expelled from the chamber 32, but in other applications it couldhave other results e.g. the generation of a volume of compressed air.The stage finishes when baffle plate 10 and work piston 14 are pushedforward against the end wall of the barrel 2 and the plunger 38 is atthe end of its travel in the dosing chamber 32 (FIG. 3 c), and thepriming piston 12 is at the end of its stroke abutting one end region ofthe barrel 2.

As shown, this embodiment does not include retaining struts to preventforward movement of the work piston 14 until a threshold pressure isreached, or a striker to improve the pressure delivery profile. Suchstruts (or other motion limiting/release mechanism) or strikercomponents could of course be incorporated if required.

An exhaust valve on the main combustion chamber 8 is now opened, againeither on a mechanical link from direct or indirect user input or on anelectrical signal from the main ignition circuit to a solenoid valve.With the valve open the baffle plate 10 is pushed away from the primingpiston 12 by the baffle plate spring, resulting in exhaustion of thecombustion gases from the main chamber.

In order to permit free forward travel of the baffle plate 10, and alsoso as to prepare for the next operation cycle, air needs to drawn intothe system. For the embodiment shown, this is achieved through an openpassage that runs from a point in the front wall of the subsidiarycombustion chamber 72 to a point in the barrel wall just in front of thebaffle plate 10. As the baffle plate is pushed backwards, air is drawnvia the subsidiary combustion chamber 72 and its open exhaust port intothe space just behind the baffle plate, in the process also replacingany remaining combustion gases in the main combustion chamber 8 with newair. Once any lost motion has been taken up, the return travel of thebaffle plate 10/work piston 14 also pulls the plunger 38 back to itsstarting position.

Once the baffle plate 10 has returned to its starting position, bothexhaust valves are closed and the system is ready to repeat the firingsequence.

It is noted that initial manual priming of this embodiment is notrequired as there is no compression of the gas in the subsidiarycombustion chamber.

The major differences between the embodiment shown in FIGS. 1 and 2 aand that depicted in FIGS. 3 a-c are:

-   -   a) the main combustion chamber 8 is disposed towards one end of        the barrel 2 in the second embodiment, and accordingly both        baffle plate 10 (and work piston 14 on which the baffle plate is        mounted), positioned to one side of the chamber 8, move in the        same direction in response to a combustive event in the chamber,        whereas in the first detailed embodiment the combustion chamber        8 is more centrally positioned within the device with the baffle        plate 10 and work piston 14 positioned on opposite sides of the        combustion chamber with the result that a combustive event in        the chamber 8 forces the baffle plate 10 and work piston 14        apart, in opposite directions.    -   b) The second main difference is the provision of a subsidiary        combustion chamber, wherein a combustive event taking place in        the subsidiary chamber provides the motive force for achieving        priming of the fuel/air mix in the main combustion chamber.    -   c) Another difference, implicit in the description above, is        that in the embodiment illustrated in FIG. 3, the baffle plate        10 is mounted on the work piston 14, whilst in the embodiment        shown in FIGS. 1 and 2 a, the baffle plate 10 is mounted on an        additional baffle plate piston, the work piston 14 being        separate.

The arrangement shown in FIGS. 3 a-c has an advantage relative to thatshown in FIGS. 1 and 2 a, in that the work piston 14 performs the dualrole of both transmitting energy from the combustion chamber 8 to thedosing chamber 32 on the “down” stroke and, on its return stroke, primesthe fuel/air mix in the combustion chamber 8 for the next cycle ofoperation. This arrangement avoids the need for a priming spring andother bulky components, with the overall result that the device can bemade much more compact than the arrangement shown in FIGS. 1 and 2 a.

Another advantage of the second embodiment, as already noted, is that aninitial manual priming of the device is not required. Yet furtheradvantages are that the trigger latch is no longer required to withstanda large force (from a powerful priming spring) and that substantiallyall of the energy of the combustion from the main combustive event (inchamber 8) can be used for the desired output without any energy beingdiverted to re-priming of the device.

1. A portable powered device, comprising: a housing; a main combustionchamber within the housing for combustion of a mixture of a fuel and acombustion-supporting gas, the combustion chamber being defined by thehousing and by a baffle plate; a priming piston in the housing on a sideof the baffle plate opposite the main combustion chamber to compress themixture of a fuel and a combustion-supporting gas to a pressure inexcess of ambient atmospheric pressure prior to combustion; a subsidiarycombustion chamber within the housing for combustion of a second mixtureof a fuel and a combustion-supporting gas, the subsidiary combustionchamber being defined by the priming piston; a work piston, extendingfrom the baffle plate, which performs the work required of the device;the work piston and the priming piston being separately movable inresponse, directly or indirectly, to combustion of the mixture of thefuel and combustion-supporting gas in the main combustion chamber andthe subsidiary combustion chamber; and whereby energy released bycombustion of the fuel and the combustion-supporting gas in thesubsidiary combustion chamber is used to compress a mixture of the fueland combustion-supporting gas in the main combustion chamber to readythe device for displacement of the work piston.
 2. A device according toclaim 1, wherein the movable baffle plate forms a gas-tight seal with aninner surface of the housing, the baffle plate comprising a one-wayvalve means which valve means permits entrance of thecombustion-supporting gas into the combustion chamber but does notpermit egress of combustion products, the baffle plate being movablefrom a first position to a second position in response to a combustiveevent within the combustion chamber; the device further comprising areturn means to return the baffle plate from the second position to thefirst position, which return movement exhausts the combustion productsfrom the combustion chamber.
 3. A device according to claim 1, wherein acombustive event within the main combustion chamber provides the powerby which the device performs its intended task and a further combustiveevent within the subsidiary combustion chamber provides, directly orindirectly, the power by which a successive fuel/combustion-supportinggas mixture is compressed for combustion in a subsequent cycle ofoperation.
 4. A device according to claim 3, wherein the main andsubsidiary combustion chambers are disposed towards opposed end regionsof the housing.
 5. A device according to claim 1, wherein the workpiston and priming piston move in the same direction in response to acombustive event in the main combustion chamber.
 6. A device inaccordance with claim 1 including means for dispensing doses of aliquid.
 7. A device according to claim 1 including means foradministering a dose of medicament to a human or animal subject.
 8. Adevice according to claim 1, comprising a multi-component work memberassembly, which components after performance of one cycle of operationare automatically returned to their starting positions ready forperformance of another cycle.